Hi,
1st off thanks for taking the time to play the game and leave feedback. It means a lot :)
You did make some good points on mechanics, being too simple, but this my 1st game so I wanted to make it pretty simple. I am thinking about adding an additional mechanic, and I'm hoping the gimmicks for the future levels will make up for that.
I'll definitely consider adding a health bar/meter for the bosses in future, so thanks for that :)